Thermoplastic molded objects, particularly those intended for use on the exterior of automobiles, are decorated by vacuum metallization to provide a bright and shiny metallic appearance. However, these molded parts frequently lack the smooth surface needed to obtain the desired bright and shiny finish, so the molded parts are coated to improve surface smoothness, and the coating is baked to cure the same. Baking at low temperature not exceeding about 170.degree. F. is required because the molded plastic parts are damaged by exposure to higher temperature. However, a baking time of about 2 hours is needed at 170.degree. F., and this holds up production and introduces large oven requirements and energy costs which are detrimental. Moreover, the prior basecoats exhibit poor humidity and salt spray resistance evidenced by delamination of the metal deposit.
The use of ultraviolet light-cured coatings is known to eliminate the need for an extended bake, but ultraviolet-cured coatings normally include residual volatile material, and thus would not be regarded as capable of withstanding a vacuum metallization process because the loss of volatiles would disrupt the coating and impair the desired bright and shiny finish. Thus, while light-cured coatings constitute a known way of eliminating prolonged baking, such coatings would not normally be regarded to be applicable to the problem under consideration.